The Hopkins Population Center (HPC) requests a five-year grant under the NICHD R24 Population Research Infrastructure Program. Grant funds will be used in part to provide research infrastructure for a multidisciplinary community of 53 highly productive researchers throughout Johns Hopkins University. Funds are also requested for HPC activities to foster innovation, new collaborations and professional development, as well as supporting institutional linkages with other research organizations in the US and abroad. The population research of HPC associates can be broadly characterized as focusing on population health, and can be categorized into three substantive areas: Poverty and its Consequences for Health and Well-Being; Sexual and Reproductive Health; and Adolescence and Transitions to Adulthood. An emerging theme is the Demography of Political Crisis. Two cross-cutting themes can also be identified in the research of HPC associates: a focus on the development and application of new methodologies, and a geographic focus on one of two resource-contained areas, sub-Saharan Africa or poor neighborhoods of Baltimore. Support is requested for three cores. The Computing Core provides a significantly enhanced Windows and Unix computing environment relative to that generally available through the University, and supports associates' research with statistical computing. The Information Services Core maintains an extensive print collection, assists associates with access to a wide range of electronic information resources, and provides document delivery and bibliographic search services. The STD and Biomarker Core provide STD diagnostic services and biomarker assays, and also works to develop new, non-invasive tests for population-based research. This revised proposal contains new research directions for HPC, supported by innovative activities such as a new system for the professional development of junior faculty. Two senior faculty, Amy Tsui and Jane Bertrand, and the programs they direct provide new opportunities for applied research and for substantial savings through cost sharing. Support through the R24 mechanism will provide crucial assistance in achieving HPC's goals.